Vegetarian Dinosaurs Were Champion Chompers

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Giant plant-eating dinosaurs may have been champion chewers up
there with the likes of mammals such as horses, bison or
elephants, researchers say.

The finding could help explain why
these behemoths dominated the plains of Europe, Asia and
North America during the last part of the age of dinosaurs,
scientists added.

Duck-billed herbivores called hadrosaurids thundered across the
world during the Late Cretaceous period, dating about 65 million
to 100 million years ago. They grazed
on horsetails, ferns and primitive flowering plantson the
ground, and browsed on Earth's conifers.

The plants these dinosaurs fed on were tough and covered with
hard, tooth-gouging particles. Hadrosaurids chewed
their meals with teeth that possessed flattened grinding
surfaces much like those of horses and bison. Some hadrosaurids
sported up to 1,400 of these teeth, and were continually
replacing them.

"They were like walking pulp mills — I suspect they could eat any
kind of plant they ran into," said researcher Gregory Erickson, a
paleobiologist at Florida State University in Tallahassee.

The chewing teeth of mammals can be relatively complex,
possessing four major types of tissue of varying hardness. These
combinations help keep the grinding ridges and valleys on a
tooth's surface from wearing and breaking down. In contrast, most
reptile teeth are comparably simple, with only two kinds of
tissue — hard enamel and a softer bone-like material. [ Paleo-Art:
Stunning Dinosaur Illustrations ]

"It didn't make sense to me that the complex surfaces we see in
hadrosaur teeth could be done with the simple tooth tissues
reptiles are supposed to have," Erickson said.

Now researchers find hadrosaurid teeth were far more complex than
those of known reptiles — they were composed of six different
types of tissue.

"They were as sophisticated, if not more sophisticated, than any
known mammal," Erickson told LiveScience.

After analyzing fossil hadrosaurid teeth with microscopy and
X-rays and by testing them with diamond-tipped probes, the
researchers found the way tissues were distributed varied
substantially within each tooth. This would allow a single tooth
to assume different forms and functions as the tooth changed over
time, exposing different surfaces as the teeth migrated across
the chewing surfaces in the mouths of the dinosaurs over time.

The complexity of hadrosaurid teeth would have proved excellent
tools for handling tough, gritty plants. This could explain why
this group of dinosaurs was so common.

Now Erickson and his colleagues plan to use these methods to
investigate teeth from both extinct and living reptile and mammal
species to see how these groups diversified in response to their
diet.